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我正在试验用Java中的switch语句，我写了下面的程序，打印出一周中一天的相应数字。我在调试程序时遇到了麻烦。下面是这样的。

public static void main(String[] args) {
    String str;

    Scanner scan = new Scanner(System.in);
    System.out.println("Please enter your day of the week: ");
    scan.next();

    switch(str) {
        case "Monday":
            System.out.println("The number corresponding to your chosen day is: 1");
            break;
        case "Tuesday":
            System.out.println("The number corresponding to your chosen day is: 2");
            break;
        case "Wednesday":
            System.out.println("The number corresponding to your chosen day is: 3");
            break;
        case "Thursday":
            System.out.println("The number corresponding to your chosen day is: 4");
            break;
        case "Friday":
            System.out.println("The number corresponding to your chosen day is: 5");
            break;
        case "Saturday":
            System.out.println("The number corresponding to your chosen day is: 6");
            break;
        case "Sunday":
            System.out.println("The number corresponding to your chosen day is: 7");
            break;
            default:
            throw new IllegalArgumentException("Invalid day of the week");

    }
}

}

错误指出 "str my not have been initialized"。然而，当我试着操作这个并初始化了 str 像这样。

String str = "Monday";

我每次都得到同样的输出。

The number corresponding to your chosen day is: 1

任何帮助都将是非常感激的，非常感谢你！

Answer 1

代码应该是这样的会工作。初始的本地变量值和从扫描对象的赋值。

public static void main(String[] args) {
    String str = null; // initialisation

    Scanner scan = new Scanner(System.in);
    System.out.println("Please enter your day of the week: ");
    str = scan.next(); //assignment

    switch(str) {
        case "Monday":
            System.out.println("The number corresponding to your chosen day is: 1");
            break;
        case "Tuesday":
            System.out.println("The number corresponding to your chosen day is: 2");
            break;
        case "Wednesday":
            System.out.println("The number corresponding to your chosen day is: 3");
            break;
        case "Thursday":
            System.out.println("The number corresponding to your chosen day is: 4");
            break;
        case "Friday":
            System.out.println("The number corresponding to your chosen day is: 5");
            break;
        case "Saturday":
            System.out.println("The number corresponding to your chosen day is: 6");
            break;
        case "Sunday":
            System.out.println("The number corresponding to your chosen day is: 7");
            break;
        default:
            throw new IllegalArgumentException("Invalid day of the week");

    }
}